# Preliminary Results (Synthetic Data) We generate a random 4-ary MRF and we sample training and test data. We forget the structure and start learning with.

## Presentation on theme: "Preliminary Results (Synthetic Data) We generate a random 4-ary MRF and we sample training and test data. We forget the structure and start learning with."— Presentation transcript:

Preliminary Results (Synthetic Data) We generate a random 4-ary MRF and we sample training and test data. We forget the structure and start learning with a fully connected but binary graph. For each data point we randomly designate each r.v. as either input, hidden or output. Training Procedure: Our training objective is: loss +.runtime We train by replacing the hard pruning threshold with a soft one, so we can compute the gradient of error and runtime w.r.t. the parameters. Gate features: Gate G AB that controls the factor between r.v.s A and B is conditioned on the values of A and B. Each r.v. (A or B) can be {0,1, hidden, output}. Gate features are the conjunction of the factor id and the two variable values. When both A and B are observed, we can just turn the factor off. The total number of features is 4x4-2x2=12. We compare evidence-specific MRF to a L1-regularized model. Preliminary Results (Synthetic Data) We generate a random 4-ary MRF and we sample training and test data. We forget the structure and start learning with a fully connected but binary graph. For each data point we randomly designate each r.v. as either input, hidden or output. Training Procedure: Our training objective is: loss +.runtime We train by replacing the hard pruning threshold with a soft one, so we can compute the gradient of error and runtime w.r.t. the parameters. Gate features: Gate G AB that controls the factor between r.v.s A and B is conditioned on the values of A and B. Each r.v. (A or B) can be {0,1, hidden, output}. Gate features are the conjunction of the factor id and the two variable values. When both A and B are observed, we can just turn the factor off. The total number of features is 4x4-2x2=12. We compare evidence-specific MRF to a L1-regularized model. Fast and Accurate Prediction via Evidence-Specific MRF Structure Veselin Stoyanov and Jason Eisner Johns Hopkins University Goal We want to learn evidence-specific structures for MRFs. I.e., different examples may rely on different factors to predict the outputs. Motivation 1.Data may be missing heterogeneously. Often the case with relational data. Our models can learn to rely more on the evidence and less on other inferred variables. 2.We want our models to perform fast test-time prediction. We are willing to trade-off some accuracy: We will optimize a interpolation of the loss function and the speed: loss +.runtime Approach 1. Gates The formalism of gates [Minka and Winn, 2008] allows us to capture contextual (in)dependencies. 2. ERMA (Empirical Risk Minimization under Approximations) We use the ERMA algorithm [Stoyanov, Ropson and Eisner, 2011] to jointly learn gate and MRF parameters by performing Empirical Risk Minimization. Goal We want to learn evidence-specific structures for MRFs. I.e., different examples may rely on different factors to predict the outputs. Motivation 1.Data may be missing heterogeneously. Often the case with relational data. Our models can learn to rely more on the evidence and less on other inferred variables. 2.We want our models to perform fast test-time prediction. We are willing to trade-off some accuracy: We will optimize a interpolation of the loss function and the speed: loss +.runtime Approach 1. Gates The formalism of gates [Minka and Winn, 2008] allows us to capture contextual (in)dependencies. 2. ERMA (Empirical Risk Minimization under Approximations) We use the ERMA algorithm [Stoyanov, Ropson and Eisner, 2011] to jointly learn gate and MRF parameters by performing Empirical Risk Minimization. Gates Gates [Minka and Winn, 2008] can capture conditional (in)dependencies. A gate is a random variable that turns a factor on or off: where In our model, gates are classifiers that decide whether a factor should be on/off based on the observation pattern (see results section). Gates can be partially on: we use the posterior marginal probability of a gate to damp down the messages through a given factor. A two-step test-time procedure: 1.Compute gate values: 2.Turn off (or damp) factors and run inference. If the gate marginal probability is low, we prune the factor, which improves speed at a slight cost to accuracy. Gates Gates [Minka and Winn, 2008] can capture conditional (in)dependencies. A gate is a random variable that turns a factor on or off: where In our model, gates are classifiers that decide whether a factor should be on/off based on the observation pattern (see results section). Gates can be partially on: we use the posterior marginal probability of a gate to damp down the messages through a given factor. A two-step test-time procedure: 1.Compute gate values: 2.Turn off (or damp) factors and run inference. If the gate marginal probability is low, we prune the factor, which improves speed at a slight cost to accuracy. AB G1G1 A C C E E D B F G7G7 G2G2 G3G3 G4G4 G5G5 G6G6 G1G1 G1G1 A C C E E D B F ERMA Empirical Risk Minimization under Approximations [Stoyanov, Ropson and Eisner, 2011] is an algorithm for learning in probabilistic graphical models by matching test-time conditions and performing empirical risk minimization. ERMA utilizes back-propagation of error to compute gradients of the output loss. Empirical evidence shows ERMA performs well on real- world problems that require approximations [Stoyanov and Eisner, 2012]. It is easy to extend ERMA so that it optimizes gate parameters and MRF parameters jointly. ERMA implementation at: http://www.clsp.jhu.edu/~ves/software ERMA Empirical Risk Minimization under Approximations [Stoyanov, Ropson and Eisner, 2011] is an algorithm for learning in probabilistic graphical models by matching test-time conditions and performing empirical risk minimization. ERMA utilizes back-propagation of error to compute gradients of the output loss. Empirical evidence shows ERMA performs well on real- world problems that require approximations [Stoyanov and Eisner, 2012]. It is easy to extend ERMA so that it optimizes gate parameters and MRF parameters jointly. ERMA implementation at: http://www.clsp.jhu.edu/~ves/software

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